You can achieve the desired functionality by using the FormatSets tool. Review the following online demo
and the followig onilne help article http://www.telerik.com/help/aspnet-ajax/editor-format-sets.html
. In addition I created a small video where you can see how to customize bullets by using the FormatSests tool http://screencast.com/t/jSj1gVHj
If you have further questions regarding the command, I will be glad to answer them.
the Telerik team
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